On July 17, 2002, at 1245 central daylight time, a Grumman G-164, N623U, piloted by a commercial pilot, was substantially damaged when it gradually descended into and impacted a field, after making an agricultural application pass, near Browning, Illinois. The airplane had departed Schuy-Rush Airport (5K4), Rushville, Illinois, for the local flight at 1230. Visual meteorological conditions prevailed. The flight was operating under provisions of 14 CFR Part 137 at the time of the accident. The pilot was not injured. The pilot stated that after making an agricultural pass he "pulled up over [the] trees and turned left . . . and got too slow, which I realized when I looked up. Aircraft settled and I dropped [the] nose to gain speed. But at [the] last second [I] pulled [the] nose up and contacted [the] ground. [The impact] spread the gear enough for the spreader to hit [the] ground, then [the] prop struck [the] ground and [the] aircraft went up on [its] nose and over on top." The pilot held a commercial pilot certificate, with an airplane--single-engine land rating, and a valid 2nd class medical certificate. He last passed a biennial flight review on August 20, 2001, and had accumulated over 4,900 hours total flight time. Of that, 2,500 hours were in the same make and model as the accident aircraft. The Grumman G-164 airplane, S/N 359, involved in the accident had completed an annual inspection on March 17, 2002, and accumulated a total time of 5,563 hours on the airframe (as reported by the pilot/owner). Eleven (11) hours of that time had been since the annual. The Pratt & Whitney, R-985 series, engine installed had accumulated 265 hours since last overhaul. The pilot did not report any malfunctions or failures associated with the aircraft or engine prior to, or at the time of, the accident. Weather conditions at the scene were reported by the pilot as clear, with fifteen (15) miles visibility, light southerly winds (2 kts) and no turbulence. Conditions at the Quincy Regional Airport (UIN), 39 nm to the south-west, were reported as clear, with ten (10) miles visibility and winds from 220 degrees at eight (8) knots by the on-field AWOS. Capital Airport (SPI), Springfield, Illinois, reported conditions as clear, with five (5) miles visibility in haze and winds from 230 degrees at seven (7) knots.